Thomas White is an associate professor in the Department of Physics, and he’s interested in learning about what’s on the inside of planets and the states of matter it exists in.
“The easiest question you might ask is, ‘Is the center of a planet a solid or a liquid?’” he said.
And that seemingly simple question, as it turns out, is really difficult to answer.
White studies the interiors of other planets using methods in laboratory astrophysics. The insides of planets can tell researchers a lot about the planet. For example, the motion of Earth’s dense, molten core inside, called a dynamo, creates a magnetic field that protects Earth’s inhabitants from dangerous solar radiation. Scientists know very little about the insides of other planets, but lab-based high energy density (HED) physics, which studies exotic states of matter, can help elucidate some of the physical processes that are happening inside.
How to study the inside of a planet, in a lab
I get to use these billion-dollar machines that are as big as three football fields and fire lasers and blow things up, which is sort of every child’s dream.
“The field is high energy density physics, and that means a lot of energy squished into a small volume,” White said. Recreating conditions inside other planets requires extremely high amounts of energy that White gets from high-powered lasers. One of those lasers is Lawrence Livermore National Laboratory’s National Ignition Facility (NIF), which was featured heavily in the news recently for accomplishing fusion with a net gain of energy. NIF is the largest and most energetic laser in the world, putting out 1.8 megajoules of energy in a pulse about 10 nanoseconds long. “When it fires, it releases more energy than the whole rest of the planet combined.”
As one might imagine, firing the NIF laser is exceptionally expensive, and is an immensely sought-after opportunity for physicists who want to study unusual states of matter, so there are few chances to use it.
“The workhorse for us is another laser, which is the OMEGA laser, which is at the Laboratory for Laser Energetics in Rochester, New York. It is the second-biggest laser, and this is much easier to get time on,” White said.
The OMEGA and NIF lasers are both optical lasers that fire energy pulses at a target, frequently made of tungsten or gold. To “see” what is happening to the target, researchers use x-rays which travel through the target and show how atoms are behaving inside.
“One of the tricks to these experiments is to create the interesting state of matter, [and then quickly] send in some x-rays to see what it looks like before it explodes.” The massive energy pulses hitting the material put it under such extreme pressure that eventually, after few nanoseconds, it explodes. To see the results of the optical laser pulses, White’s lab uses the Linac Coherent Light Source, which is a three-kilometer-long x-ray laser.
“But the problem is, they don’t have a very good optical laser there to create the states of matter [we’re interested in]. So we’re sort of in a predicament, where the best optical lasers that make the most interesting things are not located next to the best x-ray lasers to probe them.” But White takes advantage of any opportunity to use the lasers. Last November, for example, he fired the NIF laser on a piece of tungsten wire.
“I get to use these billion-dollar machines that are as big as three football fields and fire lasers and blow things up, which is sort of every child’s dream,” White said, laughing.
One of the challenges his research faces is blowing up the right stuff. Tungsten, like that in the wire he fired on at the NIF, doesn’t exist in the cores of planets. Iron does. But it’s difficult to engineer nanoscale pieces of iron. That’s a challenge White’s graduate student, Sarah has taken on. “She’s done an amazing job. We’re thinking we might be able to 3D print these things,” White said.
Having fun in astrophysics
White said that one of the best parts of the work he does is that the work changes every day, whether it’s addressing the engineering challenges of making tiny iron targets, writing code to analyze results, writing and publishing papers, or firing massive lasers. White also just finds the research fascinating and feels “incredibly lucky” to be able to do such fun, exciting work.
“We create these exquisite targets with wires in them that are one hundredth of the width of a human hair that you can’t even see, and then you take these football field-sized lasers and focus it down to create temperatures of over one hundred thousand Kelvin or even one million Kelvin on earth. Things that last for ten nanoseconds, and we take a picture of that and look at it.”
White said the field of high energy density physics has been increasing in popularity, especially with the recent fusion announcement from the NIF. Private fusion companies, national labs and academia all present opportunities to utilize a doctoral degree in HED physics.
An impressive start
He is a shining example of the kind of scientist I would like to be one day.
After graduating from Oxford with his doctoral degree in 2015 and arriving at the ΒιΆΉΣ³» in 2017, White has been recognized for numerous achievements so far in his career. In 2021 he won an NSF CAREER Award, which are given to early-career researchers who show potential for serving as role models in research and education. He was awarded the Mousel-Feltner Excellence in Research Award in 2021 as well and was awarded tenure last semester.
White was also named the Clemons-Magee Endowed Professor in Physics. This endowment is meant to support and recognize professors “who spark students’ curiosity and creativity and motivate them to pursue careers in the fields of chemistry and physics.”
White enjoys the fresh perspective that undergraduate researchers can bring to the lab. “I love having undergraduate researchers in my group. I think they keep us all young and make it a more fun place to work and I think everyone gets something out of it.”
White has received high praise for his mentorship from his undergraduates. Jacob Molina, an alumnus who is currently pursuing his Ph.D. in plasma physics at Princeton University, said of White, “Throughout our time working together, he has been incredibly patient with me, guided me through all the hardships that research may entail, and always believed in me all the moments when I did not even believe in myself; he is a shining example of the kind of scientist I would like to be one day.”
Upon receiving his professorship, White said he appreciated the recognition.
“All my graduate students want to pursue science professions when they leave, whether that be a professor or working in science at a national lab or something like that. I think part of why I got this award is that I have this [ability] that everyone who works for me wants to stay around in the field and stay around doing science. It’s nice to be recognized for that.”
